Time-multiplexed backlight, multiview display, and method

ABSTRACT

A time-multiplexed backlight and display employ a broad-angle backlight to provide broad-angle emitted light corresponding to a 2D portion of a displayed image, a multiview backlight to provide directional emitted light corresponding to a multiview portion of the displayed image, and a mode controller configured to time-multiplex the 2D portion and the multiview portion by activating the broad-angle backlight and the multiview backlight in sequential manner as a composite image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims priority toInternational Patent Application No. PCT/US2020/029017, filed Apr. 20,2020, which claims the benefit of priority to U.S. Provisional PatentApplication Ser. No. 62/837,174, filed Apr. 22, 2019, the entirecontents of both of which are herein incorporated by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

N/A

BACKGROUND

Electronic displays are a nearly ubiquitous medium for communicatinginformation to users of a wide variety of devices and products. Amongthe most commonly found electronic displays are the cathode ray tube(CRT), plasma display panels (PDP), liquid crystal displays (LCD),electroluminescent displays (EL), organic light-emitting diode (OLED)and active matrix OLEDs (AMOLED) displays, electrophoretic displays (EP)and various displays that employ electromechanical or electrofluidiclight modulation (e.g., digital micromirror devices, electrowettingdisplays, etc.). In general, electronic displays may be categorized aseither active displays (i.e., displays that emit light) or passivedisplays (i.e., displays that modulate light provided by anothersource). Among the most obvious examples of active displays are CRTs,PDPs and OLEDs/AMOLEDs. Displays that are typically classified aspassive when considering emitted light are LCDs and EP displays. Passivedisplays, while often exhibiting attractive performance characteristicsincluding, but not limited to, inherently low power consumption, mayfind somewhat limited use in many practical applications given the lackof an ability to emit light.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features of examples and embodiments in accordance with theprinciples described herein may be more readily understood withreference to the following detailed description taken in conjunctionwith the accompanying drawings, where like reference numerals designatelike structural elements, and in which:

FIG. 1A illustrates a perspective view of a multiview display in anexample, according to an embodiment consistent with the principlesdescribed herein.

FIG. 1B illustrates a graphical representation of the angular componentsof a light beam having a particular principal angular direction in anexample, according to an embodiment consistent with the principlesdescribed herein.

FIG. 2 illustrates a cross-sectional view of a diffraction grating in anexample, according to an embodiment consistent with the principlesdescribed herein.

FIG. 3A illustrates a cross-sectional view of a time-multiplexedbacklight in an example, according to an embodiment consistent with theprinciples described herein.

FIG. 3B illustrates a cross-sectional view of a time-multiplexedbacklight in another example, according to an embodiment consistent withthe principles described herein.

FIG. 3C illustrates a perspective view of a time-multiplexed backlightin an example, according to an embodiment consistent with the principlesdescribed herein.

FIG. 4 illustrates a cross-sectional view of a broad-angle backlight inan example, according to an embodiment consistent with the principlesdescribed herein.

FIG. 5A illustrates a cross-sectional view of a portion of a multiviewbacklight including a multibeam element in an example, according to anembodiment consistent with the principles described herein.

FIG. 5B illustrates a cross-sectional view of a portion of a multiviewbacklight including a multibeam element in an example, according toanother embodiment consistent with the principles described herein.

FIG. 6 illustrates a plan view of a multibeam element 124 in an example,according to an embodiment consistent with the principles describedherein.

FIG. 7 illustrates a cross-sectional view of a portion of a multiviewbacklight including a multibeam element in an example, according toanother embodiment consistent with the principles described herein.

FIG. 8 illustrates a cross-sectional view of a portion of a multiviewbacklight including a multibeam element in an example, according toanother embodiment consistent with the principles described herein.

FIG. 9 illustrates a cross-sectional view of a portion of a multiviewbacklight including a multibeam element in an example, according toanother embodiment consistent with the principles described herein.

FIG. 10 illustrates a block diagram of a time-multiplexed multiviewdisplay in an example, according to an embodiment consistent with theprinciples described herein.

FIG. 11 illustrates a flow chart of a method of time-multiplexedbacklight operation in an example, according to an embodiment consistentwith the principles described herein.

Certain examples and embodiments may have other features that are one ofin addition to and in lieu of the features illustrated in theabove-referenced figures. These and other features are detailed belowwith reference to the above-referenced figures.

DETAILED DESCRIPTION

Examples and embodiments in accordance with the principles describedherein provide time-multiplexed backlighting or time-multiplexed,mode-switching backlighting with application to a time-multiplexedmultiview display as well as methods of operation thereof. Inparticular, in accordance with the principles described herein, atime-multiplexed backlight is configured to provide broad-angle emittedlight during a two-dimensional (2D) mode and directional emitted lightcomprising directional light beams during a multiview mode. Thebroad-angle emitted light may support the display of 2D information(e.g., a 2D image or text), while the directional light beams of thedirectional emitted light may support the display of multiview orthree-dimensional (3D) information (e.g., a multiview image), forexample. Further, in various embodiments, the 2D mode and the multiviewmode of the time-multiplexed backlight are time-multiplexed ortime-interlaced to provide the broad-angle emitted light in a first timeinterval and the directional emitted light in a second time interval,respectively. According to the time-multiplexing or time-interlacing, atime-multiplexed multiview display that includes the time-multiplexedbacklight may provide a composite image that includes both a 2D contentand multiview or 3D content.

According to various embodiments, the multiview mode of atime-multiplexed multiview display may provide so-called ‘glasses-free’or autostereoscopic images, while the 2D mode may facilitate presentingof 2D information or content at a relatively higher native resolutionthan is available in the multiview mode, especially where the 2Dinformation or content that does not include or benefit from a thirddimension. As such, the composite image provided by time-multiplexingthe 2D and multiview modes may provide both high resolution 2D andsomewhat lower resolution, multiview or 3D content simultaneously in thesame image or on the same display. Uses of time-multiplexed backlightingin time-multiplexed multiview displays described herein include, but arenot limited to, mobile telephones (e.g., smart phones), watches, tabletcomputes, mobile computers (e.g., laptop computers), personal computersand computer monitors, automobile display consoles, camera displays, andvarious other mobile as well as substantially non-mobile displayapplications and devices.

Herein a ‘two-dimensional display’ or ‘2D display’ is defined as adisplay configured to provide a view of an image that is substantiallythe same regardless of a direction from which the image is viewed (i.e.,within a predefined viewing angle or range of the 2D display). A liquidcrystal display (LCD) found in many smart phones and computer monitorsare examples of 2D displays. In contrast herein, a ‘multiview display’is defined as an electronic display or display system configured toprovide different views of a multiview image in or from different viewdirections. In particular, the different views may represent differentperspective views of a scene or object of the multiview image. In someinstances, a multiview display may also be referred to as athree-dimensional (3D) display, e.g., when simultaneously viewing twodifferent views of the multiview image provides a perception of viewinga three-dimensional image.

FIG. 1A illustrates a perspective view of a multiview display 10 in anexample, according to an embodiment consistent with the principlesdescribed herein. As illustrated in FIG. 1A, the multiview display 10comprises a screen 12 to display a multiview image to be viewed. Themultiview display 10 provides different views 14 of the multiview imagein different view directions 16 relative to the screen 12. The viewdirections 16 are illustrated as arrows extending from the screen 12 invarious different principal angular directions; the different views 14are illustrated as shaded polygonal boxes at the termination of thearrows (i.e., depicting the view directions 16); and only four views 14and four view directions 16 are illustrated, all by way of example andnot limitation. Note that while the different views 14 are illustratedin FIG. 1A as being above the screen, the views 14 actually appear on orin a vicinity of the screen 12 when the multiview image is displayed onthe multiview display 10. Depicting the views 14 above the screen 12 isonly for simplicity of illustration and is meant to represent viewingthe multiview display 10 from a respective one of the view directions 16corresponding to a particular view 14.

A view direction or equivalently a light beam having a directioncorresponding to a view direction of a multiview display generally has aprincipal angular direction given by angular components {θ, ϕ}, bydefinition herein. The angular component θ is referred to herein as the‘elevation component’ or ‘elevation angle’ of the light beam. Theangular component ϕ is referred to as the ‘azimuth component’ or‘azimuth angle’ of the light beam. By definition, the elevation angle θis an angle in a vertical plane (e.g., perpendicular to a plane of themultiview display screen while the azimuth angle ϕ is an angle in ahorizontal plane (e.g., parallel to the multiview display screen plane).

FIG. 1B illustrates a graphical representation of the angular components{θ, ϕ} of a light beam 20 having a particular principal angulardirection or simply ‘direction’ corresponding to a view direction (e.g.,view direction 16 in FIG. 1A) of a multiview display in an example,according to an embodiment consistent with the principles describedherein. In addition, the light beam 20 is emitted or emanates from aparticular point, by definition herein. That is, by definition, thelight beam 20 has a central ray associated with a particular point oforigin within the multiview display. FIG. 1B also illustrates the lightbeam (or view direction) point of origin, O.

Further herein, the term ‘multiview’ as used in the terms ‘multiviewimage’ and ‘multiview display’ is defined as a plurality of viewsrepresenting different perspectives or including angular disparitybetween views of the view plurality. In addition, herein the term‘multiview’ explicitly includes more than two different views (i.e., aminimum of three views and generally more than three views), bydefinition herein. As such, ‘multiview display’ as employed herein isexplicitly distinguished from a stereoscopic display that includes onlytwo different views to represent a scene or an image. Note however,while multiview images and multiview displays may include more than twoviews, by definition herein, multiview images may be viewed (e.g., on amultiview display) as a stereoscopic pair of images by selecting onlytwo of the multiview views to view at a time (e.g., one view per eye).

A ‘multiview pixel’ is defined herein as a set of sub-pixels or ‘view’pixels in each of a similar plurality of different views of a multiviewdisplay. In particular, a multiview pixel may have individual viewpixels corresponding to or representing a view pixel in each of thedifferent views of the multiview image. Moreover, the view pixels of themultiview pixel are so-called ‘directional pixels’ in that each of theview pixels is associated with a predetermined view direction of acorresponding one of the different views, by definition herein. Further,according to various examples and embodiments, the different view pixelsof a multiview pixel may have equivalent or at least substantiallysimilar locations or coordinates in each of the different views. Forexample, a first multiview pixel may have individual view pixels locatedat {x₁y₁} in each of the different views of a multiview image, while asecond multiview pixel may have individual view pixels located at {x₂y₂}in each of the different views, and so on. In some embodiments, a numberof view pixels in a multiview pixel may be equal to a number of views ofthe multiview display.

Herein, a ‘light guide’ is defined as a structure that guides lightwithin the structure using total internal reflection or ‘TIR’. Inparticular, the light guide may include a core that is substantiallytransparent at an operational wavelength of the light guide. In variousexamples, the term ‘light guide’ generally refers to a dielectricoptical waveguide that employs total internal reflection to guide lightat an interface between a dielectric material of the light guide and amaterial or medium that surrounds that light guide. By definition, acondition for total internal reflection is that a refractive index ofthe light guide is greater than a refractive index of a surroundingmedium adjacent to a surface of the light guide material. In someembodiments, the light guide may include a coating in addition to orinstead of the aforementioned refractive index difference to furtherfacilitate the total internal reflection. The coating may be areflective coating, for example. The light guide may be any of severallight guides including, but not limited to, one or both of a plate orslab guide and a strip guide.

Further herein, the term ‘plate’ when applied to a light guide as in a‘plate light guide’ is defined as a piecewise or differentially planarlayer or sheet, which is sometimes referred to as a ‘slab’ guide. Inparticular, a plate light guide is defined as a light guide configuredto guide light in two substantially orthogonal directions bounded by atop surface and a bottom surface (i.e., opposite surfaces) of the lightguide. Further, by definition herein, the top and bottom surfaces areboth separated from one another and may be substantially parallel to oneanother in at least a differential sense. That is, within anydifferentially small section of the plate light guide, the top andbottom surfaces are substantially parallel or co-planar.

In some embodiments, the plate light guide may be substantially flat(i.e., confined to a plane) and therefore, the plate light guide is aplanar light guide. In other embodiments, the plate light guide may becurved in one or two orthogonal dimensions. For example, the plate lightguide may be curved in a single dimension to form a cylindrical shapedplate light guide. However, any curvature has a radius of curvaturesufficiently large to ensure that total internal reflection ismaintained within the plate light guide to guide light.

As defined herein, a ‘non-zero propagation angle’ of guided light is anangle relative to a guiding surface of a light guide. Further, thenon-zero propagation angle is both greater than zero and less than acritical angle of total internal reflection within the light guide, bydefinition herein. Moreover, a specific non-zero propagation angle maybe chosen (e.g., arbitrarily) for a particular implementation as long asthe specific non-zero propagation angle is less than the critical angleof total internal reflection within the light guide. In variousembodiments, the light may be introduced or coupled into the light guide122 at the non-zero propagation angle of the guided light.

According to various embodiments, guided light or equivalently a guided‘light beam’ produced by coupling light into the light guide may be acollimated light beam. Herein, a ‘collimated light’ or ‘collimated lightbeam’ is generally defined as a beam of light in which rays of the lightbeam are substantially parallel to one another within the light beam.Further, rays of light that diverge or are scattered from the collimatedlight beam are not considered to be part of the collimated light beam,by definition herein.

Herein, a ‘diffraction grating’ is generally defined as a plurality offeatures (i.e., diffractive features) arranged to provide diffraction oflight incident on the diffraction grating. In some examples, theplurality of features may be arranged in a periodic or quasi-periodicmanner. For example, the diffraction grating may include a plurality offeatures (e.g., a plurality of grooves or ridges in a material surface)arranged in a one-dimensional (1D) array. In other examples, thediffraction grating may be a two-dimensional (2D) array of features. Thediffraction grating may be a 2D array of bumps on or holes in a materialsurface, for example.

As such, and by definition herein, the ‘diffraction grating’ is astructure that provides diffraction of light incident on the diffractiongrating. If the light is incident on the diffraction grating from alight guide, the provided diffraction or diffractive scattering mayresult in, and thus be referred to as, ‘diffractive scattering’ in thatthe diffraction grating may scatter light out of the light guide bydiffraction. Further, by definition herein, the features of adiffraction grating are referred to as ‘diffractive features’ and may beone or more of at, in, and on a material surface (i.e., a boundarybetween two materials). The surface may be a surface of a light guide,for example. The diffractive features may include any of a variety ofstructures that diffract light including, but not limited to, one ormore of grooves, ridges, holes and bumps at, in or on the surface. Forexample, the diffraction grating may include a plurality ofsubstantially parallel grooves in the material surface. In anotherexample, the diffraction grating may include a plurality of parallelridges rising out of the material surface. The diffractive features(e.g., grooves, ridges, holes, bumps, etc.) may have any of a variety ofcross-sectional shapes or profiles that provide diffraction including,but not limited to, one or more of a sinusoidal profile, a rectangularprofile (e.g., a binary diffraction grating), a triangular profile and asaw tooth profile (e.g., a blazed grating).

According to various examples described herein, a diffraction grating(e.g., a diffraction grating of a multibeam element, as described below)may be employed to diffractively scatter or couple light out of a lightguide (e.g., a plate light guide) as a light beam. In particular, adiffraction angle θ_(m) of or provided by a locally periodic diffractiongrating may be given by equation (1) as:

$\begin{matrix}{\theta_{m} = {\sin^{- 1}\left( {{n\mspace{14mu}\sin\mspace{14mu}\theta_{i}} - \frac{m\;\lambda}{d}} \right)}} & (1)\end{matrix}$

where λ is a wavelength of the light, m is a diffraction order, n is anindex of refraction of a light guide, d is a distance or spacing betweenfeatures of the diffraction grating, θ is an angle of incidence of lighton the diffraction grating. For simplicity, equation (1) assumes thatthe diffraction grating is adjacent to a surface of the light guide anda refractive index of a material outside of the light guide is equal toone (i.e., n_(out)=1). In general, the diffraction order m is given byan integer. A diffraction angle θ_(m) of a light beam produced by thediffraction grating may be given by equation (1) where the diffractionorder is positive (e.g., m>0). For example, first-order diffraction isprovided when the diffraction order m is equal to one (i.e., m=1).

FIG. 2 illustrates a cross-sectional view of a diffraction grating 30 inan example, according to an embodiment consistent with the principlesdescribed herein. For example, the diffraction grating 30 may be locatedon a surface of a light guide 40. In addition, FIG. 2 illustrates alight beam 50 incident on the diffraction grating 30 at an incidentangle θ_(i). The incident light beam 50 may be a beam of guided light(i.e., a guided light beam) within the light guide 40. Also illustratedin FIG. 2 is a directional light beam 60 diffractively produced andcoupled-out by the diffraction grating 30 as a result of diffraction ofthe incident light beam 50. The directional light beam 60 has adiffraction angle θ_(m) (or ‘principal angular direction’ herein) asgiven by equation (1). The diffraction angle θ_(m) may correspond to adiffraction order ‘m’ of the diffraction grating 30, for examplediffraction order m=1 (i.e., a first diffraction order).

By definition herein, a ‘multibeam element’ is a structure or element ofa backlight or a display that produces light that includes a pluralityof light beams. In some embodiments, the multibeam element may beoptically coupled to a light guide of a backlight to provide theplurality of light beams by coupling or scattering out a portion oflight guided in the light guide. Further, the light beams of theplurality of light beams produced by a multibeam element have differentprincipal angular directions from one another, by definition herein. Inparticular, by definition, a light beam of the plurality has apredetermined principal angular direction that is different from anotherlight beam of the light beam plurality. As such, the light beam isreferred to as a ‘directional light beam’ and the light beam pluralitymay be termed a ‘directional light beam plurality,’ by definitionherein.

Furthermore, the directional light beam plurality may represent a lightfield. For example, the directional light beam plurality may be confinedto a substantially conical region of space or have a predeterminedangular spread that includes the different principal angular directionsof the light beams in the light beam plurality. As such, thepredetermined angular spread of the light beams in combination (i.e.,the light beam plurality) may represent the light field.

According to various embodiments, the different principal angulardirections of the various directional light beams of the plurality aredetermined by a characteristic including, but not limited to, a size(e.g., length, width, area, etc.) of the multibeam element. In someembodiments, the multibeam element may be considered an ‘extended pointlight source’, i.e., a plurality of point light sources distributedacross an extent of the multibeam element, by definition herein.Further, a directional light beam produced by the multibeam element hasa principal angular direction given by angular components {θ, ϕ}, bydefinition herein, and described above with respect to FIG. 1B.

Herein a ‘collimator’ is defined as substantially any optical device orapparatus that is configured to collimate light. For example, acollimator may include, but is not limited to, a collimating mirror orreflector, a collimating lens, a diffraction grating, a tapered lightguide, and various combinations thereof. According to variousembodiments, an amount of collimation provided by the collimator mayvary in a predetermined degree or amount from one embodiment to another.Further, the collimator may be configured to provide collimation in oneor both of two orthogonal directions (e.g., a vertical direction and ahorizontal direction). That is, the collimator may include a shape orsimilar collimating characteristic in one or both of two orthogonaldirections that provides light collimation, according to someembodiments.

Herein, a ‘collimation factor’ is defined as a degree to which light iscollimated. In particular, a collimation factor defines an angularspread of light rays within a collimated beam of light, by definitionherein. For example, a collimation factor σ may specify that a majorityof light rays in a beam of collimated light is within a particularangular spread (e.g., +/−a degrees about a central or principal angulardirection of the collimated light beam). The light rays of thecollimated light beam may have a Gaussian distribution in terms of angleand the angular spread may be an angle determined by at one-half of apeak intensity of the collimated light beam, according to some examples.

Herein, a ‘light source’ is defined as a source of light (e.g., anoptical emitter configured to produce and emit light). For example, thelight source may comprise an optical emitter such as a light emittingdiode (LED) that emits light when activated or turned on. In particular,herein the light source may be substantially any source of light orcomprise substantially any optical emitter including, but not limitedto, one or more of a light emitting diode (LED), a laser, an organiclight emitting diode (OLED), a polymer light emitting diode, aplasma-based optical emitter, a fluorescent lamp, an incandescent lamp,and virtually any other source of light. The light produced by the lightsource may have a color (i.e., may include a particular wavelength oflight), or may be a range of wavelengths (e.g., white light). In someembodiments, the light source may comprise a plurality of opticalemitters. For example, the light source may include a set or group ofoptical emitters in which at least one of the optical emitters produceslight having a color, or equivalently a wavelength, that differs from acolor or wavelength of light produced by at least one other opticalemitter of the set or group. The different colors may include primarycolors (e.g., red, green, blue) for example. A ‘polarized’ light sourceis defined herein as substantially any light source that produces orprovides light having a predetermined polarization. For example, thepolarized light source may comprise a polarizer at an output of anoptical emitter of the light source.

Herein, a ‘multiview image’ is defined as a plurality of images (i.e.,greater than three images) wherein each image of the pluralityrepresents a different view corresponding to a different view directionof the multiview image. As such, the multiview image is a collection ofimages (e.g., two-dimensional images) which, when display on a multiviewdisplay, may facilitate a perception of depth and thus appear to be animage of a 3D scene to a viewer, for example.

By definition, ‘broad-angle’ emitted light is defined as light having acone angle that is greater than a cone angle of the view of a multiviewimage or multiview display. In particular, in some embodiments, thebroad-angle emitted light may have a cone angle that is greater thanabout twenty degrees (e.g., >±20°). In other embodiments, thebroad-angle emitted light cone angle may be greater than about thirtydegrees (e.g., >±30°), or greater than about forty degrees(e.g., >±40°), or greater than about fifty degrees (e.g., >±50°). Forexample, the cone angle of the broad-angle emitted light may be greaterthan about sixty degrees (e.g., >±60°).

In some embodiments, the broad-angle emitted light cone angle maydefined to be about the same as a viewing angle of an LCD computermonitor, an LCD tablet, an LCD television, or a similar digital displaydevice meant for broad-angle viewing (e.g., about ±40-65°). In otherembodiments, broad-angle emitted light may also be characterized ordescribed as diffuse light, substantially diffuse light, non-directionallight (i.e., lacking any specific or defined directionality), or aslight having a single or substantially uniform direction.

Embodiments consistent with the principles described herein may beimplemented using a variety of devices and circuits including, but notlimited to, one or more of integrated circuits (ICs), very large scaleintegrated (VLSI) circuits, application specific integrated circuits(ASIC), field programmable gate arrays (FPGAs), digital signalprocessors (DSPs), graphical processor unit (GPU), and the like,firmware, software (such as a program module or a set of instructions),and a combination of two or more of the above. For example, anembodiment or elements thereof may be implemented as circuit elementswithin an ASIC or a VLSI circuit. Implementations that employ an ASIC ora VLSI circuit are examples of hardware-based circuit implementations.

In another example, an embodiment may be implemented as software using acomputer programming language (e.g., C/C++) that is executed in anoperating environment or a software-based modeling environment (e.g.,MATLAB®, MathWorks, Inc., Natick, Mass.) that is further executed by acomputer (e.g., stored in memory and executed by a processor or agraphics processor of a general purpose computer). Note that one or morecomputer programs or software may constitute a computer-programmechanism, and the programming language may be compiled or interpreted,e.g., configurable or configured (which may be used interchangeably inthis discussion), to be executed by a processor or a graphics processorof a computer.

In yet another example, a block, a module or an element of an apparatus,device or system (e.g., image processor, camera, etc.) described hereinmay be implemented using actual or physical circuitry (e.g., as an IC oran ASIC), while another block, module or element may be implemented insoftware or firmware. In particular, according to the definitionsherein, some embodiments may be implemented using a substantiallyhardware-based circuit approach or device (e.g., ICs, VLSI, ASIC, FPGA,DSP, firmware, etc.), while other embodiments may also be implemented assoftware or firmware using a computer processor or a graphics processorto execute the software, or as a combination of software or firmware andhardware-based circuitry, for example.

Further, as used herein, the article ‘a’ is intended to have itsordinary meaning in the patent arts, namely ‘one or more’. For example,‘a multibeam element’ means one or more multibeam elements and as such,‘the multibeam element’ means ‘the multibeam element(s)’ herein. Also,any reference herein to ‘top’, ‘bottom’, ‘upper’, ‘lower’, ‘up’, ‘down’,‘front’, back’, ‘first’, ‘second’, ‘left’ or ‘right’ is not intended tobe a limitation herein. Herein, the term ‘about’ when applied to a valuegenerally means within the tolerance range of the equipment used toproduce the value, or may mean plus or minus 10%, or plus or minus 5%,or plus or minus 1%, unless otherwise expressly specified. Further, theterm ‘substantially’ as used herein means a majority, or almost all, orall, or an amount within a range of about 51% to about 100%. Moreover,examples herein are intended to be illustrative only and are presentedfor discussion purposes and not by way of limitation.

In accordance with some embodiments of the principles described herein,a time-multiplexed backlight is provided. FIG. 3A illustrates across-sectional view of a time-multiplexed backlight 100 in an example,according to an embodiment consistent with the principles describedherein. FIG. 3B illustrates a cross-sectional view of a time-multiplexedbacklight 100 in another example, according to an embodiment consistentwith the principles described herein. In particular, FIG. 3A illustratesthe time-multiplexed backlight 100 during or according to a first ortwo-dimensional (2D) mode. FIG. 3B illustrates the time-multiplexedbacklight 100 during or according to a second or multiview mode. FIG. 3Cillustrates a perspective view of a time-multiplexed backlight 100 in anexample, according to an embodiment consistent with the principlesdescribed herein. The time-multiplexed backlight 100 is illustrated inFIG. 3C during the multiview mode, by way of example and not limitation.Further, the 2D and multiview modes may be time-multiplexed intime-sequential or time-interlaced manner to provide the 2D andmultiview modes in alternating first and second time intervals (e.g.,alternating between FIGS. 3A and 3B), according to various embodiments.As such, the time-multiplexed backlight 100 may also be referred to as a‘time-multiplexed, mode-switching’ backlight.

As illustrated, the time-multiplexed backlight 100 is configured toprovide or emit light as emitted light 102. The emitted light 102 may beused to illuminate an electronic display that employs thetime-multiplexed backlight 100, according to various examples andembodiments. For example, the emitted light 102 may be used toilluminate an array of light valves (e.g., light valves 106, describedbelow) of the electronic display. Further, in some embodiments, theelectronic display that employs the time-multiplexed backlight 100 maybe configured to alternate between the display of a two-dimensional (2D)image and a multiview image using the emitted light 102 in or duringsequential time intervals. Moreover, according to time-multiplexing ortime-interlacing in the sequential time intervals, the 2D images andmultiview images may be provided a composite image that includes both 2Dand multiview content or information, as is described further below.

In particular, according to the two operational modes of thetime-multiplexed backlight 100, the emitted light 102 may have orexhibit different characteristics, according to time multiplexing. Thatis, light emitted by the time-multiplexed backlight 100 as the emittedlight 102 may comprise light that is either directional or substantiallynon-directional, according to the two different modes. For example, asdescribed below in more detail, in the 2D mode, time-multiplexedbacklight 100 is configured to provide the emitted light 102 asbroad-angle emitted light 102′. Alternatively, in the multiview mode,the time-multiplexed backlight 100 is configured to provide the emittedlight 102 as directional emitted light 102″.

According to various embodiments, the directional emitted light 102″provided during the multiview mode comprises a plurality of directionallight beams having principal angular directions that differ from oneanother. Further, directional light beams of the directional emittedlight 102″ have directions corresponding to different view directions ofa multiview image. Conversely, the broad-angle emitted light 102′ islargely non-directional and further generally has a cone angle that isgreater than a cone angle of a view of the multiview image or multiviewdisplay associated with the time-multiplexed backlight 100, according tovarious embodiments. During operation of the time-multiplexed backlight100, the 2D mode may be activated in a first time interval and themultiview mode may be activated in a second time interval. Further, thefirst and second time intervals are interlaced with one another in asequential manner according to time-multiplexing, in variousembodiments.

The broad-angle emitted light 102′ is illustrated in FIG. 3A during thefirst time interval as dashed arrows for ease of illustration. However,the dashed arrows representing the broad-angle emitted light 102′ arenot meant to imply any particular directionality of the emitted light102, but instead merely represent the emission and transmission oflight, e.g., from the time-multiplexed backlight 100. Similarly, FIGS.3B and 3C illustrate the directional light beams of the directionalemitted light 102″ during the second time interval as a plurality ofdiverging arrows. As described above, the different principal angulardirections of directional light beams of the directional emitted light102″ emitted during the multiview mode correspond to respective viewdirections of a multiview image or equivalently of a multiview display.Further, the directional light beams may be or represent a light field,in various embodiments. In some embodiments, the broad-angle emittedlight 102′ and the directional emitted light 102″ directional lightbeams of the emitted light 102 may be modulated (e.g., using lightvalves 106, as described below) to facilitate the display of informationhaving one or both of 2D content and multiview or 3D image content.

As illustrated in FIGS. 3A-3C, the time-multiplexed backlight 100comprises a broad-angle backlight 110. The illustrated broad-anglebacklight 110 has a planar or substantially planar light-emittingsurface 110′ configured to provide the broad-angle emitted light 102′during the 2D mode (e.g., see FIG. 3A). According to variousembodiments, the broad-angle backlight 110 may be substantially anybacklight having a light-emitting surface 110′ configured to providelight to illuminate an array of light valves of a display. For example,the broad-angle backlight 110 may be a direct-emitting or directlyilluminated planar backlight. Direct-emitting or directly illuminatedplanar backlights include, but are not limited to, a backlight panelemploying a planar array of cold-cathode fluorescent lamps (CCFLs), neonlamps or light emitting diodes (LEDs) configured to directly illuminatethe planar light-emitting surface 110′ and provide the broad-angleemitted light 102′. An electroluminescent panel (ELP) is anothernon-limiting example of a direct-emitting planar backlight. In otherexamples, the broad-angle backlight 110 may comprise a backlight thatemploys an indirect light source. Such indirectly illuminated backlightsmay include, but are not limited to, various forms of edge-coupled orso-called ‘edge-lit’ backlights.

FIG. 4 illustrates a cross-sectional view of a broad-angle backlight 110in an example, according to an embodiment consistent with the principlesdescribed herein. As illustrated in FIG. 4, the broad-angle backlight110 is an edge-lit backlight and comprises a light source 112 coupled toan edge of the broad-angle backlight 110. The edge-coupled light source112 is configured to produce light within the broad-angle backlight 110.Further, as illustrated by way of example and not limitation, thebroad-angle backlight 110 comprises a guiding structure 114 (or lightguide) having a substantially rectangular cross section with parallelopposing surfaces (i.e., a rectangular-shaped guiding structure) alongwith a plurality of extraction features 114 a. The broad-angle backlight110 illustrated in FIG. 4 comprises extraction features 114 a at asurface (i.e., top surface) of the guiding structure 114 of thebroad-angle backlight 110, by way of example and not limitation. Lightfrom the edge-coupled light source 112 and guided within therectangular-shaped guiding structure 114 may be redirected, scatteredout of or otherwise extracted from the guiding structure 114 by theextraction features 114 a to provide the broad-angle emitted light 102′,according to various embodiments. The broad-angle backlight 110 isactivated by activating or turning on the edge-coupled light source 112,e.g., illustrated in FIG. 3A using cross-hatching.

In some embodiments, the broad-angle backlight 110, whetherdirect-emitting or edge-lit (e.g., as illustrated in FIG. 4), mayfurther comprise one or more additional layers or films including, butnot limited to, a diffuser or diffusion layer, a brightness enhancementfilm (BEF), and a polarization recycling film or layer. For example, adiffuser may be configured to increase an emission angle of thebroad-angle emitted light 102′ when compared to that provided by theextraction features 114 a alone. The brightness enhancement film may beused to increase an overall brightness of the broad-angle emitted light102′, in some examples. Brightness enhancement films (BEF) areavailable, for example, from 3M Optical Systems Division, St. Paul,Minn. as a Vikuiti™ BEF II which are micro-replicated enhancement filmsthat utilize a prismatic structure to provide up to a 60% brightnessgain. The polarization recycling layer may be configured to selectivelypass a first polarization while reflecting a second polarization backtoward the rectangular-shaped guiding structure 114. The polarizationrecycling layer may comprise a reflective polarizer film or dualbrightness enhancement film (DBEF), for example. Examples of DBEF filmsinclude, but are not limited to, 3M Vikuiti™ Dual Brightness EnhancementFilm available from 3M Optical Systems Division, St. Paul, Minn. Inanother example, an advanced polarization conversion film (APCF) or acombination of brightness enhancement and APCF films may be employed asthe polarization recycling layer.

FIG. 4 illustrates the broad-angle backlight 110 further comprising adiffuser 116 adjacent to guiding structure 114 and the planarlight-emitting surface 110′ of the broad-angle backlight 110. Further,illustrated in FIG. 4 are a brightness enhancement film 117 and apolarization recycling layer 118, both of which are also adjacent to theplanar light-emitting surface 110′. In some embodiments, the broad-anglebacklight 110 further comprises a reflective layer 119 adjacent to asurface of the guiding structure 114 opposite to the planarlight-emitting surface 110′ (i.e., on a back surface), e.g., asillustrated in FIG. 4. The reflective layer 119 may comprise any of avariety of reflective films including, but not limited to, a layer ofreflective metal or an enhanced specular reflector (ESR) film. Examplesof ESR films include, but are not limited to, a Vikuiti™ EnhancedSpecular Reflector Film available from 3M Optical Systems Division, St.Paul, Minn.

Referring again to FIGS. 3A-3C, the time-multiplexed backlight 100further comprises a multiview backlight 120. As illustrated, themultiview backlight 120 comprises an array of multibeam elements 124.Multibeam elements 124 of the multibeam element array are spaced apartfrom one another across the multiview backlight 120, according tovarious embodiments. For example, in some embodiments, the multibeamelements 124 may be arranged in a one-dimensional (1D) array. In otherembodiments, the multibeam elements 124 may be arranged in atwo-dimensional (2D) array. Further, differing types of multibeamelements 124 may be utilized in the multiview backlight 120 including,but limited to, active emitters and various scattering elements as setforth below in connection with FIGS. 5A-10. According to variousembodiments, each multibeam element 124 of the multibeam element arrayis configured to provide a plurality of directional light beams havingdirections corresponding to different view directions of a multiviewimage during a multiview mode. In particular, directional light beams ofthe directional light beam plurality comprise the directional emittedlight 102″ provided during the multiview mode, according to variousembodiments.

In some embodiments (e.g., as illustrated), the multiview backlight 120further comprises a light guide 122 configured to guide light as guidedlight 104. The light guide 122 may be a plate light guide, in someembodiments. According to various embodiments, the light guide 122 isconfigured to guide the guided light 104 along a length of the lightguide 122 according to total internal reflection. A general propagationdirection 103 of the guided light 104 within the light guide 122 isillustrated by a bold arrow in FIG. 3B. In some embodiments, the guidedlight 104 may be guided in the propagation direction 103 at a non-zeropropagation angle and may comprise collimated light that is collimatedaccording to a predetermined collimation factor σ, as illustrated inFIG. 3B.

In various embodiments, the light guide 122 may include a dielectricmaterial configured as an optical waveguide. The dielectric material mayhave a first refractive index that is greater than a second refractiveindex of a medium surrounding the dielectric optical waveguide. Adifference in refractive indices is configured to facilitate totalinternal reflection of the guided light 104 according to one or moreguided modes of the light guide 122, for example. In some embodiments,the light guide 122 may be a slab or plate optical waveguide comprisingan extended, substantially planar sheet of optically transparent,dielectric material. According to various examples, the opticallytransparent material of the light guide 122 may include or be made up ofany of a variety of dielectric materials including, but not limited to,one or more of various types of glass (e.g., silica glass,alkali-aluminosilicate glass, borosilicate glass, etc.) andsubstantially optically transparent plastics or polymers (e.g.,poly(methyl methacrylate) or ‘acrylic glass’, polycarbonate, etc.). Insome examples, the light guide 122 may further include a cladding layer(not illustrated) on at least a portion of a surface (e.g., one or bothof the top surface and the bottom surface) of the light guide 122. Thecladding layer may be used to further facilitate total internalreflection, according to some examples.

In embodiments that include the light guide 122, a multibeam element 124of the multibeam element array may be configured to scatter out aportion of the guided light 104 from within the light guide 122 and todirect the scattered out portion away from a first surface 122′ of thelight guide 122 or equivalent from a first surface of the multiviewbacklight 120 to provide the directional emitted light 102″, asillustrated in FIG. 3B. For example, the guided light portion may bescattered out by the multibeam element 124 through the first surface122′. Further, as illustrated in FIGS. 3A-3C, a second surface of themultiview backlight 120 opposite to the first surface may be adjacent tothe planar light-emitting surface 110′ of the broad-angle backlight 110,according to various embodiments.

Note that the plurality of directional light beams of the directionalemitted light 102″, as illustrated in FIG. 3B, is or represents theplurality of directional light beams having different principal angulardirections, described above. That is, a directional light beam has adifferent principal angular direction from other directional light beamsof the directional emitted light 102″, according to various embodiments.Further, the multiview backlight 120 may be substantially transparent(e.g., in at least the 2D mode) to allow the broad-angle emitted light102′ from the broad-angle backlight 110 to pass or be transmittedthrough a thickness of the multiview backlight 120, as illustrated inFIG. 3A by the dashed arrows that originate at the broad-angle backlight110 and subsequently pass through the multiview backlight 120. In otherwords, the broad-angle emitted light 102′ provided by the broad-anglebacklight 110 is configured to be transmitted through the multiviewbacklight 120 during the 2D mode, e.g., by virtue of the multiviewbacklight transparency.

For example, the light guide 122 and the spaced apart plurality ofmultibeam elements 124 may allow light to pass through the light guide122 through both the first surface 122′ and the second surface 122″.Transparency may be facilitated, at least in part, due to both therelatively small size of the multibeam elements 124 and the relativelylarge inter-element spacing of the multibeam element 124. Further,especially when the multibeam elements 124 comprise diffraction gratingsas described below, the multibeam elements 124 may also be substantiallytransparent to light propagating orthogonal to the light guide surfaces122′, 122″, in some embodiments. Thus, for example, light from thebroad-angle backlight 110 may pass in the orthogonal direction throughthe light guide 122 with the multibeam element array of the multiviewbacklight 120, according to various embodiments.

In some embodiments (e.g., as illustrated in FIGS. 3A-3C), the multiviewbacklight 120 may further comprise a light source 126. As such, themultiview backlight 120 may be an edge-lit backlight, for example.According to various embodiments, the light source 126 is configured toprovide the light to be guided within light guide 122. In particular,the light source 126 may be located adjacent to an entrance surface orend (input end) of the light guide 122. In various embodiments, thelight source 126 may comprise substantially any source of light (e.g.,optical emitter) including, but not limited to, one or more lightemitting diodes (LEDs) or a laser (e.g., laser diode). In someembodiments, the light source 126 may comprise an optical emitterconfigured produce a substantially monochromatic light having anarrowband spectrum denoted by a particular color. In particular, thecolor of the monochromatic light may be a primary color of a particularcolor space or color model (e.g., a red-green-blue (RGB) color model).In other examples, the light source 126 may be a substantially broadbandlight source configured to provide substantially broadband orpolychromatic light. For example, the light source 126 may provide whitelight. In some embodiments, the light source 126 may comprise aplurality of different optical emitters configured to provide differentcolors of light. The different optical emitters may be configured toprovide light having different, color-specific, non-zero propagationangles of the guided light corresponding to each of the different colorsof light. As illustrated in FIG. 3B, activation of the multiviewbacklight 120 may comprise activating the light source 126, illustratedusing cross-hatching in FIG. 3B.

In some embodiments, the light source 126 may further comprise acollimator (not illustrated). The collimator may be configured toreceive substantially uncollimated light from one or more of the opticalemitters of the light source 126. The collimator is further configuredto convert the substantially uncollimated light into collimated light.In particular, the collimator may provide collimated light having thenon-zero propagation angle and being collimated according to apredetermined collimation factors, according to some embodiments.Moreover, when optical emitters of different colors are employed, thecollimator may be configured to provide the collimated light having oneor both of different, color-specific, non-zero propagation angles andhaving different color-specific collimation factors. The collimator isfurther configured to communicate the collimated light to the lightguide 122 to propagate as the guided light 104, described above.

As illustrated in FIGS. 3A-3B, the time-multiplexed backlight 100further comprises a mode controller 130. The mode controller 130 isconfigured to time-multiplex the 2D mode and multiview mode bysequentially activating the broad-angle backlight 110 during a firsttime interval and activating the multiview backlight 120 during a secondtime interval. In particular, according to some embodiments, the modecontroller 130 may be configured to switch between the 2D mode and themultiview mode by sequentially activating a light source 112 of thebroad-angle backlight 110 to provide the broad-angle emitted light 102′during the 2D mode and a light source 126 of the multiview backlight 120to provide the directional emitted light 102″ during the multiview mode.Activating the light source 112 during the first time interval isillustrated by cross-hatching of the light source 112 in FIG. 3A andactivating the light source 126 during the second time interval isillustrated by cross-hatching of the light source 126 in FIG. 3B.

In some embodiments, the mode controller 130 may be configured to switchbetween or time multiplex the 2D mode and the multiview mode at one ormore predetermined frequencies, such as at a frequency selected toeffectively display images of both modes concurrently via an array oflight valves 106 for display to a viewer. By way of example, the arrayof light valves 106 may be an LCD panel operating at 120 Hz and the modecontroller 130 may switch between the 2D mode and the multiview mode at60 Hz (i.e., by sequentially activating each of the light source 112 ofthe broad-angle backlight 110 and the light source 126 of the multiviewbacklight 120 at about 60 Hz), to provide time-multiplexing. In anotherexample, the LCD panel or light valve array may operate at 240 Hz andthe 2D and multiview modes may be time-multiplexed at 120 Hz by the modecontroller 130. According to some embodiments, the 2D mode and themultiview mode may be time-multiplexed by the mode controller 130 at amaximum rate corresponding to the highest switching speed or frequencyat which the array of light valves is capable of operating while stillbeing capable of providing images to a viewer, i.e., dependent upon thetype and technology of the display. In certain embodiments,time-multiplexing of 2D and multiview modes provides the 2D image andthe multiview image that are superimposed with each other on atime-multiplexed multiview display to provide a composite image. If theswitching rate or activation rate of the 2D and multiview modes at leastexceeds for each mode the visual persistence of a viewer using thedisplay, each of the 2D image and the multiview image will appear to theuser as being constantly present and without perceptible flicker in thecomposite image. A switching rate of at least about 60 Hz for each ofthe 2D mode and the multiview mode will provide this visual persistencegoal (i.e., about or less than 1 millisecond in each mode).

Further, as mentioned above and according to various embodiments,multiview backlight 120 comprises the array of multibeam elements 124.According to some embodiments (e.g., as illustrated in FIGS. 3A-3C),multibeam elements 124 of the multibeam element array may be located atthe first surface 122′ of the light guide 122 (e.g., adjacent to thefirst surface of the multiview backlight 120). In other embodiments (notillustrated), the multibeam elements 124 may be located within the lightguide 122. In yet other embodiments (not illustrated), the multibeamelements 124 may be located at or on the second surface 122″ of thelight guide 122 (e.g., adjacent to the second surface of the multiviewbacklight 120). Further, a size of the multibeam element 124 iscomparable to a size of a light valve of a multiview display configuredto display the multiview image. That is, the multibeam element size iscomparable to a light valve size of a light valve array in a multiviewdisplay that includes the time-multiplexed backlight 100 and multiviewbacklight 120 thereof, for example.

FIGS. 3A-3C also illustrate an array of light valves 106 (e.g., of themultiview display), by way of example and not limitation. In variousembodiments, any of a variety of different types of light valves may beemployed as the light valves 106 of the light valve array including, butnot limited to, one or more of liquid crystal light valves,electrophoretic light valves, and light valves based on or employingelectrowetting. Further, as illustrated, there may be one unique set oflight valves 106 for each multibeam element 124 of the array ofmultibeam elements. The unique set of light valves 106 may correspond toa multiview pixel 106′ of the multiview display, for example.

Herein, the ‘size’ may be defined in any of a variety of manners toinclude, but not be limited to, a length, a width or an area. Forexample, the size of a light valve may be a length thereof and thecomparable size of the multibeam element 124 may also be a length of themultibeam element 124. In another example, size may refer to an areasuch that an area of the multibeam element 124 may be comparable to anarea of the light valve. In some embodiments, the size of the multibeamelement 124 is comparable to the light valve size such that themultibeam element size is between about twenty-five percent (25%) andabout two hundred percent (200%) of the light valve size. For example,if the multibeam element size is denoted ‘s’ and the light valve size isdenoted ‘S’ (e.g., as illustrated in FIG. 3B), then the multibeamelement size s may be given by equation (1) as

¼S≤s≤2S  (2)

In other examples, the multibeam element size is greater than aboutfifty percent (50%) of the light valve size, or about sixty percent(60%) of the light valve size, or about seventy percent (70%) of thelight valve size, or greater than about eighty percent (80%) of thelight valve size, or greater than about ninety percent (90%) of thelight valve size, and the multibeam element is less than about onehundred eighty percent (180%) of the light valve size, or less thanabout one hundred sixty percent (160%) of the light valve size, or lessthan about one hundred forty percent (140%) of the light valve size, orless than about one hundred twenty percent (120%) of the light valvesize. For example, by ‘comparable size’, the multibeam element size maybe between about seventy-five percent (75%) and about one hundred fifty(150%) of the light valve size. In another example, the multibeamelement 124 may be comparable in size to the light valve where themultibeam element size is between about one hundred twenty-five percent(125%) and about eighty-five percent (85%) of the light valve size.According to some embodiments, the comparable sizes of the multibeamelement 124 and the light valve may be chosen to reduce, or in someexamples to minimize, dark zones between views of the multiview display,while at the same time reducing, or in some examples minimizing, anoverlap between views of the multiview display or equivalent of themultiview image.

Note that, as illustrated in FIG. 3B, the size (e.g. width) of amultibeam element 124 may correspond to a size (e.g., width) of a lightvalve 106 in the light valve array. In other examples, the multibeamelement size may be defined as a distance (e.g., a center-to-centerdistance) between adjacent light valves 106 of the light valve array.For example, the light valves 106 may be smaller than thecenter-to-center distance between the light valves 106 in the lightvalve array. Further, a spacing between adjacent multibeam elements ofthe multibeam element array may be commensurate with a spacing betweenadjacent multiview pixels of the multiview display. For example, aninter-emitter distance (e.g., center-to-center distance) between a pairof adjacent multibeam elements 124 may be equal to an inter-pixeldistance (e.g., a center-to-center distance) between a correspondingadjacent pair of multiview pixels, e.g., represented by sets of lightvalves of the array of light valves 106. As such, the multibeam elementsize may be defined as either the size of the light valve 106 itself ora size corresponding to the center-to-center distance between the lightvalves 106, for example.

In some embodiments, a relationship between the multibeam elements 124of the plurality and corresponding multiview pixels 106′ (e.g., sets oflight valves 106) may be a one-to-one relationship. That is, there maybe an equal number of multiview pixels 106′ and multibeam elements 124.FIG. 3C explicitly illustrates by way of example the one-to-onerelationship where each multiview pixel 106′ comprising a different setof light valves 106 is illustrated as surrounded by a dashed line. Inother embodiments (not illustrated), the number of multiview pixels 106′and multibeam elements 124 may differ from one another.

In some embodiments, an inter-element distance (e.g., center-to-centerdistance) between a pair of adjacent multibeam elements 124 of theplurality may be equal to an inter-pixel distance (e.g., acenter-to-center distance) between a corresponding adjacent pair ofmultiview pixels 106′, e.g., represented by light valve sets. In otherembodiments (not illustrated), the relative center-to-center distancesof pairs of multibeam elements 124 and corresponding light valve setsmay differ, e.g., the multibeam elements 124 may have an inter-elementspacing (i.e., center-to-center distance) that is one of greater than orless than a spacing (i.e., center-to-center distance) between lightvalve sets representing multiview pixels 106′.

In some embodiments, a shape of the multibeam element 124 is analogousto a shape of the multiview pixel 106′ or equivalently, a shape of a set(or ‘sub-array’) of the light valves 106 corresponding to the multiviewpixel 106′. For example, the multibeam element 124 may have a squareshape and the multiview pixel 106′ (or an arrangement of a correspondingset of light valves 106) may be substantially square. In anotherexample, the multibeam element 124 may have a rectangular shape, i.e.,may have a length or longitudinal dimension that is greater than a widthor transverse dimension. In this example, the multiview pixel 106′ (orequivalently the arrangement of the set of light valves 106)corresponding to the multibeam element 124 may have an analogousrectangular shape. FIG. 3C illustrates a perspective view ofsquare-shaped multibeam elements 124 and corresponding square-shapedmultiview pixels 106′ comprising square sets of light valves 106. In yetother examples (not illustrated), the multibeam elements 124 and thecorresponding multiview pixels 106′ have various shapes including or atleast approximated by, but not limited to, a triangular shape, ahexagonal shape, and a circular shape.

Further (e.g., as illustrated in FIG. 3B), each multibeam element 124may be configured to provide directional emitted light 102″ to one andonly one multiview pixel 106′, according to some embodiments. Inparticular, for a given one of the multibeam elements 124, thedirectional emitted light 102″ having different principal angulardirections corresponding to the different views of the multiview displayare substantially confined to a single corresponding multiview pixel106′ and the light valves 106 thereof, i.e., a single set of lightvalves 106 corresponding to the multibeam element 124, as illustrated inFIG. 3B. As such, each multibeam element 124 of the broad-anglebacklight 110 provides a corresponding plurality of directional lightbeams of the directional emitted light 102″ that has a set of thedifferent principal angular directions corresponding to the differentviews of the multiview image (i.e., the set of directional light beamscontains a light beam having a direction corresponding to each of thedifferent view directions).

According to various embodiments, the multibeam elements 124 of themultiview backlight 120 may comprise any of a number of differentstructures configured to scatter out a portion of the guided light 104.For example, the different structures may include, but are not limitedto, diffraction gratings, micro-reflective elements, micro-refractiveelements, or various combinations thereof. In some embodiments, themultibeam element 124 comprising a diffraction grating is configured todiffractively couple or scatter out the guided light portion as thedirectional emitted light 102″ comprising a plurality of directionallight beams having the different principal angular directions. In someembodiments, a diffraction grating of a multibeam element may comprise aplurality of individual sub-gratings. In other embodiments, themultibeam element 124 comprising a micro-reflective element isconfigured to reflectively couple or scatter out the guided lightportion as the plurality of directional light beams, or the multibeamelement 124 comprising a micro-refractive element is configured tocouple or scatter out the guided light portion as the plurality ofdirectional light beams by or using refraction (i.e., refractivelyscatter out the guided light portion).

FIG. 5A illustrates a cross-sectional view of a portion of a multiviewbacklight 120 including a multibeam element 124 in an example, accordingto an embodiment consistent with the principles described herein. FIG.5B illustrates a cross-sectional view of a portion of a multiviewbacklight 120 including a multibeam element 124 in an example, accordingto another embodiment consistent with the principles described herein.In particular, FIGS. 5A-5B illustrate the multibeam element 124 of themultiview backlight 120 comprising a diffraction grating 124 a. Thediffraction grating 124 a is configured to diffractively couple orscatter out a portion of the guided light 104 as the plurality ofdirectional light beams of the directional emitted light 102″. Thediffraction grating 124 a comprises a plurality of diffractive featuresspaced apart from one another by a diffractive feature spacing (or adiffractive feature pitch or grating pitch) configured to providediffractive scattering out of the guided light portion. According tovarious embodiments, the spacing or grating pitch of the diffractivefeatures in the diffraction grating 124 a may be sub-wavelength (i.e.,less than a wavelength of the guided light 104).

In some embodiments, the diffraction grating 124 a of the multibeamelement 124 may be located at or adjacent to a surface of the lightguide 122. For example, the diffraction grating 124 a may be at oradjacent to the first surface 122′ of the light guide 122, asillustrated in FIG. 5A. The diffraction grating 124 a at the firstsurface 122′ of the light guide 122 may be a transmission modediffraction grating configured to diffractively scatter out the guidedlight portion through the first surface 122′ as the directional lightbeams of the directional emitted light 102″. In another example, asillustrated in FIG. 5B, the diffraction grating 124 a may be located ator adjacent to the second surface 122′ of the light guide 122. Whenlocated at the second surface 122″, the diffraction grating 124 a may bea reflection mode diffraction grating. As a reflection mode diffractiongrating, the diffraction grating 124 a is configured to both diffractthe guided light portion and reflect the diffracted guided light portiontoward the first surface 122′ to exit through the first surface 122′ asthe directional light beams of the directional emitted light 102″. Inother embodiments (not illustrated), the diffraction grating may belocated between the surfaces of the light guide 122, e.g., as one orboth of a transmission mode diffraction grating and a reflection modediffraction grating. Note that, in some embodiments described herein,the principal angular directions of the directional light beams of thedirectional emitted light 102″ may include an effect of refraction dueto the directional light beams exiting the light guide 122 at a lightguide surface. For example, FIG. 5B illustrates refraction (i.e.,bending) of the directional light beams due to a change in refractiveindex as the directional emitted light 102″ crosses the first surface122′. Also see FIGS. 6 and 7, described below.

According to some embodiments, the diffractive features of thediffraction grating 124 a may comprise one or both of grooves and ridgesthat are spaced apart from one another. The grooves or the ridges maycomprise a material of the light guide 122, e.g., may be formed in asurface of the light guide 122. In another example, the grooves or theridges may be formed from a material other than the light guidematerial, e.g., a film or a layer of another material on a surface ofthe light guide 122.

In some embodiments, the diffraction grating 124 a of the multibeamelement 124 is a uniform diffraction grating in which the diffractivefeature spacing is substantially constant or unvarying throughout thediffraction grating 124 a. In other embodiments, the diffraction grating124 a may be a chirped diffraction grating. By definition, the ‘chirped’diffraction grating is a diffraction grating exhibiting or having adiffraction spacing of the diffractive features (i.e., the gratingpitch) that varies across an extent or length of the chirped diffractiongrating. In some embodiments, the chirped diffraction grating may haveor exhibit a ‘chirp’ of or change in the diffractive feature spacingthat varies linearly with distance. As such, the chirped diffractiongrating is a ‘linearly chirped’ diffraction grating, by definition. Inother embodiments, the chirped diffraction grating of the multibeamelement 124 may exhibit a non-linear chirp of the diffractive featurespacing. Various non-linear chirps may be used including, but notlimited to, an exponential chirp, a logarithmic chirp or a chirp thatvaries in another, substantially non-uniform or random but stillmonotonic manner. Non-monotonic chirps such as, but not limited to, asinusoidal chirp or a triangle or sawtooth chirp, may also be employed.Combinations of any of these types of chirps may also be employed.

In some embodiments, the diffraction grating 124 a may comprise aplurality or an array of diffraction gratings or equivalently aplurality or an array of sub-gratings. Further, according to someembodiments, a differential density of sub-gratings within thediffraction grating 124 a between different multibeam elements 124 ofthe multibeam element plurality may be configured to control a relativeintensity of the plurality of directional light beams of the directionalemitted light 102″ that is diffractively scattered out by respectivedifferent multibeam elements 124. In other words, the multibeam elements124 may have different densities of sub-gratings within the diffractiongratings 124 a, respectively, and the different sub-grating densitiesmay be configured to control the relative intensity of the plurality ofdirectional light beams. In particular, a multibeam element 124 havingfewer sub-gratings within the diffraction grating 124 a may produce aplurality of directional light beams of the directional emitted light102″ having a lower intensity (or beam density) than another multibeamelement 124 having relatively more sub-gratings.

FIG. 6 illustrates a plan view of a multibeam element 124 in an example,according to an embodiment consistent with the principles describedherein. As illustrated, the multibeam element 124 comprises adiffraction grating 124 a having a plurality of sub-gratings. Inaddition, the diffraction grating 124 a has locations 123 without asub-grating to facilitate control of a density of sub-gratings and, inturn, control a relative intensity of scattering by the diffractiongrating 124 a, as illustrated in FIG. 6. FIG. 6 also illustrates a sizesof the multibeam element 124.

FIG. 7 illustrates a cross-sectional view of a portion of a multiviewbacklight 120 including a multibeam element 124 in an example, accordingto another embodiment consistent with the principles described herein.FIG. 8 illustrates a cross-sectional view of a portion of a multiviewbacklight 120 including a multibeam element 124 in an example, accordingto another embodiment consistent with the principles described herein.In particular, FIGS. 7 and 8 illustrate various embodiments of themultibeam element 124 comprising a micro-reflective element 124 b.Micro-reflective elements used as or in the multibeam element 124 mayinclude, but are not limited to, a reflector that employs a reflectivematerial or layer thereof (e.g., a reflective metal) or a reflectorbased on total internal reflection (TIR). According to some embodiments(e.g., as illustrated in FIGS. 7-8), the multibeam element 124comprising the micro-reflective element 124 b may be located at oradjacent to a surface (e.g., the second surface 122″) of the light guide122. In other embodiments (not illustrated), the micro-reflectiveelement 124 b may be located within the light guide 122 between thefirst and second surfaces 122′, 122″. In some embodiments,micro-reflective element 124 b of the multibeam element 124 may beconfigured to scatter guided light 104 incident from differentdirections, as illustrated in FIGS. 7 and 8 by a pair of arrowsrepresenting a first propagation direction 103 and a second propagationdirection 103′ of the guided light 104.

FIG. 9 illustrates a cross-sectional view of a portion of a multiviewbacklight 120 including a multibeam element 124 in an example, accordingto another embodiment consistent with the principles described herein.In particular, FIG. 9 illustrates a multibeam element 124 comprising amicro-refractive element 124 c. According to various embodiments, themicro-refractive element 124 c is configured to refractively couple orscatter out a portion of the guided light 104 from the light guide 122.That is, the micro-refractive element 124 c is configured to employrefraction (e.g., as opposed to diffraction or reflection) to couple orscatter out the guided light portion from the light guide 122 as thedirectional emitted light 102″ comprising the directional light beams,as illustrated in FIG. 9. The micro-refractive element 124 c may havevarious shapes including, but not limited to, a semi-spherical shape, arectangular shape or a prismatic or an inverted prismatic shape (i.e., ashape having sloped facets). According to various embodiments, themicro-refractive element 124 c may extend or protrude out of a surface(e.g., the first surface 122′) of the light guide 122, as illustrated,or may be a cavity in the surface (not illustrated). Further, themicro-refractive element 124 c may comprise a material of the lightguide 122, in some embodiments. In other embodiments, themicro-refractive element 124 c may comprise another material adjacentto, and in some examples, in contact with the light guide surface.

According to some embodiments of the principles described herein, atime-multiplexed multiview display is provided. The time-multiplexedmultiview display is configured to emit modulated light corresponding toor representing pixels of a two-dimensional (2D) image comprising 2Dinformation (e.g., 2D images, text, etc.) in a two-dimensional (2D) modeof the time-multiplexed multiview display. In a multiview mode, thetime-multiplexed multiview display is configured to emit modulateddirectional emitted light corresponding to or representing pixels ofdifferent views (view pixels) of a multiview image. For example, thetime-multiplexed multiview display may represent an autostereoscopic orglasses-free 3D electronic display in the multiview mode. For example,different ones of the modulated, differently directed light beams of thedirectional emitted light may correspond to different ‘views’ associatedwith the multiview information or multiview image, according to variousexamples. The different views may provide a ‘glasses free’ (e.g.,autostereoscopic, holographic, etc.) representation of information beingdisplayed by the time-multiplexed multiview display in the multiviewmode, for example. Further, the first and multiview modes aretime-multiplexed (e.g., interlaced) to allow time-interlacedpresentation of 2D and multiview information superimposed on thetime-multiplexed multiview display as composite images, according tovarious embodiments.

FIG. 10 illustrates a block diagram of a time-multiplexed multiviewdisplay 200 in an example, according to an embodiment consistent withthe principles described herein. The time-multiplexed multiview display200 may be used to present as a composite image both 2D information andmultiview information such as, but not limited to, 2D images, text, andmultiview images, according to various embodiments. In particular, thetime-multiplexed multiview display 200 illustrated in FIG. 10 isconfigured to emit modulated light 202 comprising modulated broad-angleemitted light 202′ during the 2D mode (2D), the modulated broad-angleemitted light 202′ representing 2D pixels of a 2D image, for example.Further, during the multiview mode (Multiview) the time-multiplexedmultiview display 200 illustrated in FIG. 10 is configured to emitmodulated light 202 comprising modulated directional emitted light 202″including directional light beams with different principal angulardirections representing directional pixels of a multiview image. Inparticular, the different principal angular directions may correspond tothe different view directions of different views of the multiview imagedisplayed by time-multiplexed multiview display 200 in the multiviewmode. According to various embodiments, the composite image is providedby time-multiplexing or time-interlacing the 2D mode and the multiviewmode to combine the 2D pixel of the 2D image and the directional pixelsof the multiview image on the time-multiplexed multiview display 200, asillustrated by circular arrows in FIG. 10.

As illustrated in FIG. 10, the time-multiplexed multiview display 200comprises a broad-angle backlight 210. The broad-angle backlight 210 isconfigured to provide broad-angle emitted light 204 during the 2D mode.In some embodiments, the broad-angle backlight 210 may be substantiallysimilar to the broad-angle backlight 110 of the time-multiplexedbacklight 100, described above. For example, the broad-angle backlightmay comprise a light guide having a light extraction layer configured toextract light from the rectangular-shaped light guide and to redirectthe extracted light through the diffuser as the broad-angle emittedlight 204.

The time-multiplexed multiview display 200 illustrated in FIG. 10further comprises a multiview backlight 220. As illustrated, themultiview backlight 220 comprises a light guide 222 and an array ofmultibeam elements 224 spaced apart from one another. The array ofmultibeam elements 224 is configured to scatter out guided light fromthe light guide 222 as directional emitted light 206 during themultiview mode (Multiview). According to various embodiments, thedirectional emitted light 206 provided by an individual multibeamelement 224 of the array of multibeam elements 224 comprises a pluralityof directional light beams having different principal angular directionscorresponding to view directions of the multiview image displayed by thetime-multiplexed multiview display 200 in or during the multiview mode.

In some embodiments, the multiview backlight 220 may be substantiallysimilar to the multiview backlight 120 of the above-describedtime-multiplexed backlight 100. In particular, the light guide 222 andmultibeam elements 224 may be substantially similar to theabove-described the light guide 122 and multibeam elements 124,respectively. For example, the light guide 222 may be a plate lightguide. Further, a multibeam element 224 of the array of multibeamelements 224 may comprises one or more of a diffraction grating, amicro-reflective element and a micro-refractive element opticallyconnected to the light guide 222 to scatter out the guided light as thedirectional emitted light 206, according to various embodiments.

As illustrated, the time-multiplexed multiview display 200 furthercomprises a light valve array 230. The light valve array 230 isconfigured to modulate the broad-angle emitted light 204 to provide atwo-dimensional (2D) image during the 2D mode and to modulate thedirectional emitted light 206 to provide a multiview image during themultiview mode. In particular, the light valve array 230 is configuredto receive and modulate the broad-angle emitted light 204 to provide themodulated broad-angle emitted light 202′ during the 2D mode. Similarly,the light valve array 230 is configured to receive and modulate thedirectional emitted light 206 during the multiview mode to provide themodulated directional emitted light 202″. In some embodiments, the lightvalve array 230 may be substantially similar to the array of lightvalves 106, described above with respect to the time-multiplexedbacklight 100. For example, a light valve of the light valve array maycomprise a liquid crystal light valve. Further, a size of a multibeamelement 224 of the array of multibeam elements 224 may be comparable toa size of a light valve of the light valve array 230 (e.g., between onequarter and two times the light valve size), in some embodiments.

In various embodiments, the multiview backlight 220 may be locatedbetween the planar light-emitting surface of the broad-angle backlight210 and the light valve array 230. The multiview backlight 220 may bepositioned adjacent to the broad-angle backlight 210 or separated by anarrow gap. Further, in some embodiments, the multiview backlight 220and the broad-angle backlight 210 are superimposed or stacked such thata top surface of the broad-angle backlight 210 is substantially parallelto a bottom surface of the multiview backlight 220. As such, thebroad-angle emitted light 204 from the broad-angle backlight 210 isemitted from the top surface of the broad-angle backlight 210 into andthrough the multiview backlight 220. According to various embodiments,the multiview backlight 220 is transparent to the broad-angle emittedlight 204 emitted during the 2D mode.

The time-multiplexed multiview display 200 illustrated in FIG. 10further comprises a mode controller 240. In some embodiments, the modecontroller 240 may be substantially similar to the mode controller 130of the time-multiplexed backlight 100, described above. For example, themode controller 240 is configured to sequentially activate thebroad-angle backlight 210 and the multiview backlight 220. According tovarious embodiments, the 2D image and multiview image are superimposedon the time-multiplexed multiview display 200 as a composite image. Aswith the mode controller 130, above, the mode controller 240 of FIG. 10may be configured to switch between the 2D mode and the multiview modeby sequentially activating a light source of the broad-angle backlight210 to provide broad-angle emitted light 204 during the 2D mode and alight source of the multiview backlight 220 to provide the directionalemitted light 206 during the multiview mode. According to variousembodiments, both the directional emitted light 206 and the broad-angleemitted light 204 may be modulated by the light valve array to providethe images comprising the multiview portion and the 2D portion of thecomposite image in a time-multiplexed manner.

In particular, the mode controller 240 may time-multiplex the 2D andmultiview modes of the broad-angle backlight 210 and the multiviewbacklight 220 and simultaneously control modulation of the emitted lightby the light valve array to produce the composite image, according tovarious embodiments. That is, mode switching between the 2D mode and themultiview mode may be implemented by time-multiplexing the 2D images andthe multiview images in a manner synchronized or coordinated withoperation of the light valve array 230, to provide 2D and multiviewcontent as the composite image.

For example, the two sets of images may be time-interlaced in connectionwith operating light valves of the light valve array 230 to displayrespective 2D or multiview images, so that it appears as if both imagesare being displayed simultaneously. In some embodiments, the modecontroller 240 may synchronize control of light sources of thebroad-angle backlight 210 and the multiview backlight 220 with controlof light valves of the light valve array 230 to achieve time-interlaceddisplay of the two images. In some embodiments, selected light valves ofthe light valve array 230 may be operated (turned off or on) to displaythe 2D imagery during the first time interval, followed by operation ofselected light valves to display the multiview imagery during the secondtime interval. In practice, the rate of speed at which the modecontroller 240 operates the 2D and multiview backlights is maintained ata level that allows the light valves of the light valve array 230 toswitch fully open, or fully closed, as dictated by the physics of thelight valves or pixels, such as the electric field(s) involved with theswitching. The mode controller 130 discussed above in connection withFIGS. 3A-3C may operate consistent with one or more of the abovetechniques and principles, as well. In particular, the mode controller240 may be implemented one or both of as hardware comprising circuitry(e.g., an ASIC) and modules comprising software or firmware that areexecuted by a processor or similar circuitry to various operationalcharacteristics of the mode controller 240.

In accordance with other embodiments of the principles described herein,a method of time-multiplexed backlight operation is provided. Inparticular, the method of time-multiplexed backlight operation may haveat least two modes, namely a 2D mode and a multiview mode, which aretime-multiplexed or time-interlaced. The 2D mode may display atwo-dimensional (2D) image, while the multiview mode may display athree-dimensional (3D) or a multiview image, according to variousembodiments. Time-multiplexing combines the 2D image and the 3D ormultiview image as a composite image having both 2D and multiviewcontent or information.

FIG. 11 illustrates a flow chart of a method 300 of time-multiplexedbacklight operation in an example, according to an embodiment consistentwith the principles described herein. As illustrated in FIG. 11, themethod of time-multiplexed backlight operation comprises providing 310broad-angle emitted light during a 2D mode using a broad-anglebacklight. In some embodiments, the broad-angle backlight may besubstantially similar to the broad-angle backlight 110 of thetime-multiplexed backlight 100, described above. Further, the 2D modeand the emitted broad-angle light may be substantially similar torespective ones of the 2D mode (e.g., in FIGS. 3A-3C, and the 2D Mode ofFIG. 10) and the broad-angle emitted light 204, 102′ described abovewith respect to the time-multiplexed backlights and displays, accordingto some embodiments.

The method 300 of time-multiplexed backlight operation further comprisesproviding 320 directional emitted light during a multiview mode using amultiview backlight having an array of multibeam elements spaced apartfrom one another. According to various embodiments, the directionalemitted light comprises a plurality of directional light beams providedby each multibeam element of the multibeam element array. Directions ofdirectional light beams of the directional light beam pluralitycorrespond to different view directions of a multiview image, accordingto various embodiments. In some embodiments, the multiview backlight maybe substantially similar to the multiview backlights described above,such as in connection with FIGS. 3A-3C and 11. Similarly, the multiviewmode may be substantially similar to the multiview mode of thetime-multiplexed backlight 100 described above with respect to FIGS.3A-3C as well as the multiview mode of FIG. 10, according to someembodiments. In some embodiments, the multiview backlight may bepositioned adjacent to the emission surface of the broad-angle backlightand be transparent to the broad-angle emitted light during the 2D mode.

The method 300 of time-multiplexed backlight operation further comprisestime-multiplexing 330 the 2D mode and the multiview mode using a modecontroller to sequentially activate the broad-angle backlight during afirst sequential time interval corresponding to the 2D mode and themultiview backlight during a second sequential time intervalcorresponding to the multiview mode. In some embodiments, the modecontroller may be substantially similar to the mode controller 130, 240described above. In particular, the mode controller may be implementedone or both of as hardware comprising circuitry (e.g., an ASIC) andmodules comprising software or firmware that are executed by a processoror similar circuitry to perform the actions of the mode controller.

In some embodiments (not illustrated), providing 320 the plurality ofdirectional light beams comprises guiding light in a light guide asguided light and scattering out a portion of the guided light usingmultibeam elements of the multibeam element array. Further, eachmultibeam element of the multibeam element array may comprise one ormore of a diffraction grating, a micro-refractive element, and amicro-reflective element, in some embodiments. In particular, themultiview elements of the multibeam element array may be substantiallysimilar to the multibeam elements 124 of the above-described multiviewbacklight 120, in some embodiments. The method 300 of time-multiplexedbacklight operation may further comprise providing light to the lightguide, the guided light within the light guide being collimatedaccording to a predetermined collimation factor as described above, insome embodiments.

According to some embodiments, the method 300 of time-multiplexedbacklight operation further comprises modulating the broad-angle emittedlight using an array of light valves to provide a 2D image during the 2Dmode and modulating the plurality of directional light beams using thelight valve array to provide a multiview image during the multiviewmode. In some of these embodiments, the time-multiplexing the 2D modeand the multiview mode may superimpose the 2D image and multiview imagesto provide a composite image comprising both 2D content and multiviewcontent. In some other embodiments, a size of a multibeam element of themultibeam element array may be configured as between one quarter and twotimes a size of a light valve of the light valve array. In someembodiments, the array of light valves may be substantially similar tothe array of light valves 106, described above with respect to thetime-multiplexed backlight 100.

Thus, there have been described examples and embodiments of atime-multiplexed backlight, a time-multiplexed multiview display, and amethod of time-multiplexed backlight operation that provide a pair ofmodes configured to operate in a time-multiplexed or time-interlacedmanner. It should be understood that the above-described examples aremerely illustrative of some of the many specific examples andembodiments that represent the principles described herein. Clearly,those skilled in the art can readily devise numerous other arrangementswithout departing from the scope as defined by the following claims.

What is claimed is:
 1. A time-multiplexed backlight comprising: abroad-angle backlight configured to provide broad-angle emitted lightfrom an emission surface during a two-dimensional (2D) mode; a multiviewbacklight comprising an array of multibeam elements, each multibeamelement of the multibeam element array being configured to provide aplurality of directional light beams having directions corresponding todifferent view directions of a multiview image during a multiview mode;and a mode controller configured to time-multiplex the 2D and multiviewmodes by sequentially activating the broad-angle backlight during afirst time interval and the multiview backlight during a second timeinterval, wherein the multiview backlight is disposed adjacent to theemission surface of the broad-angle backlight and is transparent to thebroad-angle emitted light during the 2D mode.
 2. The time-multiplexedbacklight of claim 1, wherein the multiview backlight further comprises:a light guide configured to guide light as guided light; and wherein thearray of multibeam elements are spaced apart from one another across thelight guide, each multibeam element of the multibeam element array beingconfigured to scatter out a portion of the guided light from the lightguide as the plurality of directional light beams.
 3. Thetime-multiplexed backlight of claim 2, wherein the light guide isconfigured to guide the guided light according to a predeterminedcollimation factor as collimated guided light.
 4. The time-multiplexedbacklight of claim 2, wherein multibeam elements of the multibeamelement array comprise one or more of a diffraction grating configuredto diffractively scatter out the guided light, a micro-reflectiveelement configured to reflectively scatter out the guided light, and amicro-refractive element configured to refractively scatter out theguided light.
 5. The time-multiplexed backlight of claim 4, wherein thediffraction grating of a multibeam element of the multibeam elementarray comprises a plurality of individual sub-gratings.
 6. Thetime-multiplexed backlight of claim 1, wherein the mode controller isconfigured to switch between the 2D mode and the multiview mode bysequentially activating a light source of the broad-angle backlight toprovide the broad-angle emitted light during the 2D mode and a lightsource of the multiview backlight to provide the plurality ofdirectional light beams during the multiview mode.
 7. A time-multiplexedmultiview display comprising the time-multiplexed backlight of claim 1,the time-multiplexed multiview display further comprising: an array oflight valves configured to modulate the broad-angle emitted light duringthe 2D mode to provide a 2D image and to modulate the plurality ofdirectional light beams during the multiview mode to provide themultiview image.
 8. The time-multiplexed multiview display of claim 7,wherein the mode controller is configured to sequentially activate thebroad-angle backlight during the first time interval to provide the 2Dimage and the multiview backlight during the second time interval toprovide the multiview image, the 2D image and the multiview image beingsuperimposed with each other on the time-multiplexed multiview displayto provide a composite image.
 9. The time-multiplexed multiview displayof claim 7, wherein a size of each multibeam element of the multibeamelement array is between one quarter and two times a size of a lightvalve of the light valve array.
 10. A time-multiplexed multiview displaycomprising: a broad-angle backlight configured to provide broad-angleemitted light; a multiview backlight comprising an array of multibeamelements, each multibeam element being configured to provide directionallight beams having directions corresponding to different view directionsof a multiview image; an array of light valves configured to modulatethe broad-angle emitted light to provide a 2D image and to modulate thedirectional light beams to provide the multiview image; and a modecontroller configured to sequentially activate the broad-angle backlightand the multiview backlight, the 2D image and multiview image beingsuperimposed on the time-multiplexed multiview display as a compositeimage.
 11. The time-multiplexed multiview display of claim 10, whereinthe multiview backlight further comprises: a light guide configured toguide light as guided light; and wherein the array of multibeam elementsare spaced apart from one another across the light guide, each multibeamelement of the multibeam element array being configured to scatter out aportion of the guided light from the light guide as the directionallight beams.
 12. The time-multiplexed multiview display of claim 11,wherein the light guide is configured to guide the guided lightaccording to a collimation factor as collimated guided light, andwherein a size of each multibeam element of the multibeam element arrayis between one quarter and two times a size of a light valve of thelight valve array.
 13. The time-multiplexed multiview display of claim11, wherein each multibeam element of the multibeam element arraycomprises one or more of a diffraction grating configured todiffractively scatter out the guided light, a micro-reflective elementconfigured to reflectively scatter out the guided light, and amicro-refractive element configured to refractively scatter out theguided light.
 14. The time-multiplexed multiview display of claim 11,wherein the mode controller is configured to activate a light source ofthe broad-angle backlight to provide the broad-angle emitted light andto activate a light source of the multiview backlight to providedirectional light beams to sequentially activate the broad-anglebacklight and the multiview backlight.
 15. The time-multiplexedmultiview display of claim 10, wherein the multiview backlight isdisposed between the broad-angle backlight and the light valve array,the multiview backlight being transparent to the broad-angle emittedlight.
 16. A method of operating a time-multiplexed backlight, themethod comprising: providing broad-angle emitted light during a 2D modeusing a broad-angle backlight; providing directional emitted lightduring a multiview mode using a multiview backlight having an array ofmultibeam elements, the directional emitted light comprising a pluralityof directional light beams provided by each multibeam element of themultibeam element array; and time multiplexing the 2D and multiviewmodes using a mode controller to sequentially activate the broad-anglebacklight during a first sequential time interval corresponding to the2D mode and the multiview backlight during a second sequential timeinterval corresponding to the multiview mode, wherein directions of theplurality of directional light beams correspond to different viewdirections of a multiview image.
 17. The method of operating atime-multiplexed backlight of claim 16, wherein providing directionalemitted light comprises: guiding light in a light guide as guided light;and scattering out a portion of the guided light as the directionalemitted light using multibeam elements of the multibeam element array,each multibeam element of the multibeam element array comprising one ormore of a diffraction grating, a micro-refractive element, and amicro-reflective element.
 18. The method of operating a time-multiplexedbacklight of claim 17, further comprising providing light to the lightguide, the guided light within the light guide being collimatedaccording to a predetermined collimation factor.
 19. The method ofoperating a time-multiplexed backlight of claim 16, further comprising:modulating the broad-angle emitted light using an array of light valvesto provide a 2D image during the 2D mode; and modulating the pluralityof directional light beams of the directional emitted light using thelight valve array to provide a multiview image during the multiviewmode, wherein time-multiplexing the 2D mode and the multiview modesuperimposes the 2D image and multiview images to provide a compositeimage comprising both 2D content and multiview content.
 20. The methodof operating a time-multiplexed backlight of claim 19, wherein a size ofa multibeam element of the multibeam element array is between onequarter and two times a size of a light valve of the light valve array.